Cytokines are biologically active macromolecules present in or released from cells. Most of them are polypeptide-like species, such as interleukins, interferons, colony-stimulating factor (CSF), and tumor necrosis factor (TNF). They are not expressed or expressed in a low amount in normal body, but are transcribed and translated in abnormal states (disease or infection). Cytokines regulate or modulate cellular responses in inflammatory or immune responses. They activate biological responses by binding to the specific receptors on the surfaces of the sensitive cells. Since cytokines often have their receptors on various target cells, pleiotropic effects of the responses are common features for a cytokine. A second messenger can also be generated through other cytokines or cytokine receptors.
For a highly active cytokine, there must be a mechanism by which its release is controlled and its activities are constrained. The biosynthesis and release of a cytokine can be regulated strictly by other cytokines or exogenous factors. Two mechanisms for controlling the activities of a cytokine have been found: the first is a receptor antagonist (inhibitory protein type I) which has a structure homologous to that of the cytokine and can bind to the receptor molecule, but does not trigger signal transduction, thus exerting inhibition by competing with the cytokine; the second is a soluble receptor molecule (inhibitory protein type II) which competes with the cellular receptor for cytokine binding, thus exerting inhibition. A large amount of experiments have shown that the two suppressive responses have a physiological correlation. At present, it has been believed that inhibitor type II has a neutralizing effect similar to that of a buffer solution, which in turn limits the systemic effect of a cytokine. Meanwhile, it also allows the cytokine to rise locally to a high concentration, thereby enhancing a paracrine effect. Their recombinant forms have pharmacological activities.
Interleukin 1 (IL-1) is involved in a wide variety of physiological processes. By inducing secretion of the neutral proteases and other cytokines (tumor necrosis factor TNF), IL-1 stimulates proliferation of various hematopoietic cells and other cells, regulates pro-inflammatory responses, and mediates damage to tissues in an inflammation, including stimulating proliferation of the synoviocytes and the chondrocytes and production of PGE2, collagenase, phospholipase A, etc, inducing inflammation in a joint; facilitates release of neutrophils from the bone marrow, induces chemotaxis and infiltration of mononuclear cells and the multinucleated granulocytes into an inflammatory site, releases lysosomal enzymes locally, causes de-granulation of the basophils and the mast cells, releases inflammatory mediators, etc. IL-1 can impose damage directly on β cells which produce insulin in the pancreatic islet. The diseases associated with IL-1 comprise rheumatoid arthritis, diabetes mellitus, systemic lupus erythematosus, dermatosclerosis and other immune diseases.
IL-1 includes two relevant factors: IL-1α and IL-1β. Furthermore, there is a relevant polypeptide known as IL-1 receptor antagonist (IL-1Ra). Both IL-1a and IL-1β exert their biological activities by binding to IL-1 receptor (IL-1R) on the cellular surface and signaling into the interior of a cell via a signal transduction system. Two types of IL-1R have been found: type I receptor (IL-1RI) and type II receptor (IL-1R II). The type I receptor, also known as T-cell receptor, has a signal transduction function; whereas the type II receptor, also known as B-cell receptor, can bind to IL-1, but does not transduce the signal. In fact, IL-1RII acts as an attenuator of IL-1, which can be designated as a “trapping” receptor. When IL-1 binds to IL-1R I, a complex is formed and then binds to a IL-1R accessory protein (IL-1R AcP) with a high affinity. The IL-1 signal transduction is activated probably by a heterodimer formed by association of the intracellular portion of the IL-1R I with the IL-1R-AcP. Furthermore, the extracellular portions of the IL-1R are also known as the soluble receptors, that is, type I soluble receptor (sIL-1RI) and type II soluble receptor (sIL-1RII), which exist in the circulation system of the body both in the normal state and in the diseased cases and can bind to IL-1α, IL-1β, or IL-1Ra to act as a natural “buffer”.
Arend, et al. (“Interleukin 1 receptor antagonist: A new member of the interleukin 1 family.” J Clin Invest, 1991,88(5): 1445-1451) has found a substance present in the cell culture supernatant and the body fluid and having an activity of inhibiting IL-1 and designated it as IL-1Ra. Eisenberg, et al. (“Interleukin 1 receptor antagonist is a member of the interleukin 1 gene family: evolution of a cytokine control mechanism.” PNAS, 1991, 88(12): 5 232-5236) has found by molecular clone technology that the gene for IL-1Ra is 1.8 kb in length, having an open reading frame encoding 177 of amino acids; and the mature form of the IL-1Ra protein has 152 of amino acids and also has a leader sequence of 25 amino acids in length. IL-1Ra has 26%-30% homology with IL-1β, and 19% with IL-1α, with a gene structure similar to that of IL-1. Therefore, it can be postulated that the portion in which the IL-1Ra shares structural similarity with the IL-1 performs a receptor-binding function, but does not activate signal transduction across the membrane. In a pathologic state, macrophages in many tissues such as synovium and dermal tissues can produce IL-1Ra. Both the human's normal skin and the cultured keratinocytes and monocytes express IL-1Ra mRNA. Although IL-1Ra has no agonism in itself upon binding to IL-1 receptor, it can eliminate or alleviate the biological effects of the IL-1, thereby affecting pathophysiological processes in the body. The equilibrium between IL-1 and IL-1Ra determines the role of IL-1 in an inflammatory process.
Many experiments have demonstrated that IL-1Ra exerts various effects, such as suppressing generation of prostaglandins, inducing a NO concentration in the serum, reducing the amount of the expressed cyclooxygenase-2 and collagenase-1, preventing the leucocytes from infiltration and the proteoglycans in joint cartilage from degradation, antagonizing an effect of IL-1β that promote the expression of the nerve growth factor, etc., which implies a wide prospect for the use of IL-1Ra in treating inflammatory diseases such as rheumatoid arthritis, amyloidosis, osteoarthritis, allergic encephalomyelitis, etc. IL-1Ra can also improve nephritis, dermatitis and respiratory inflammation, decrease the mortality of the septic shock, increase survival rate of the heat shock, suppress growth of the myeloma, and increase the success rate of the corneal homotransplantation. Likely, some agents which can induce expression of the IL-1Ra, including the human blood serum IgA, corticosteroids, non-steroid anti-inflammatory drugs such as mofezolac, IL-4, IL-13, IFN, TGF-β, IL-6, and other cytokines performing signal transduction through gp130, are useful in treating diseases caused by IL-1.
The trade name of IL-1Ra is Kineret. Kineret (generic name: Anakinra), which has been developed by Amgen, USA, is a non-glycosylated recombinant human IL-1Ra (rhIL-1Ra) having a molecular weight of 17.3 KD and consisting of 153 amino acids. The major difference between Kineret and the endogenous human IL-1Ra is that the former has one methionine residue at its N-terminus. On Nov. 14, 2001, Kineret was approved by FDA for marketing to treat adults with moderately to severely active rheumatoid arthritis who have had an absence of clinical improvement of symptoms in therapy with one or more disease-modifying anti-rheumatic drugs (DMARDs), so as to alleviate their symptoms. European Medicines Agency (EMA) has approved Kineret on Nov. 21, 2001 to be used in combination with methotrexate in patients who are not responsive adequately to treatment with methotrexate alone. At present, Kineret is under clinical trials for inflammatory bowel disease (IBD), asthma, and transplant rejection.
The onset of diabetes is associated with the impaired function of pancreatic islet β cells, and the function of pancreatic islet β cells will deteriorate progressively as pathological state extends. Currently it had been discovered that, in type 1 diabetes resulting from the destruction and the impaired functions of β cells caused by inflammation of pancreatic islet β cells, the pro-inflammatory factor IL-1β plays a key role in suppressing the functions of pancreatic islet β cells and facilitating apoptosis thereof. In patients with type 2 diabetes, it has been observed also that the expression of IL-1 in the pancreatic islet β cells is enhanced while the expression of IL-1Ra is reduced. Insufficiency of IL-1Ra appears to be a genetic property, since the genetic polymorphisms of the gene encoding IL-1Ra and the altered content of the serum IL-1Ra are correlated. IL-1β can improve the expression of the inflammatory cytokines in pancreatic islet, increase infiltration of the immune cells, leading to inflammation in the tissue, and affect the functions of β cells and the insulin sensitivity. In studies, the long-term exposure to high concentrations of glucose and a peptide hormone leptin secreted by adipose tissues would induce β cells and the pancreatic islet to produce and release IL-1β, which in turn causes the impaired functions and apoptosis of the β cells. Exogenous addition of an IL-1 receptor antagonist, such as IL-1Ra, can protect the β cells from the damage caused by high concentrations of glucose and leptin, and reduce the inflammatory marker of patients with type 2 diabetes. Similar studies also demonstrated that inflammatory mediator generated within the pancreatic islet is closely-related to diabetes (Boni-Schnetzler, et al, “Increased Interleukin (IL)-1β Messenger Ribonucleic Acid Expression in β-Cells of Individuals with Type 2 Diabetes and Regulation of IL-1β in Human Islets by Glucose and Autostimulation.” J Clin Endocrinol Metab, 2008, 93(10): 4065-4074; Donath, et al, “Islet Inflammation Impairs the Pancreatic β-Cell in Type 2 Diabetes.” Physiology (Bethesda). 2009, 24:325-331).
In one study (Ehses et al, “IL-1 antagonism reduces hyperglycemia and tissue inflammation in the type 2 diabetic GK rat”, PNAS, 2009, 106(33): 13998-14003), researchers had investigated intensively the effects of IL-1 on generation of inflammatory cytokines in pancreatic islet and inflammation in peripheral tissues responsive to insulin. GK rats, which are spontaneous, nonobese model of type 2 diabetes and develop inflammation in the pancreatic islet and the insulin resistance in peripheral tissues (liver, skeletal muscles, and adipose tissues), were chose by the researchers as the object of study. It had been found that IL-1β is expressed highly in the pancreatic islet and hepatic tissues of GK rats and that administration of IL-1Ra to the rats can block specifically the activity of IL-1 and reduce the release of inflammatory cytokines from the pancreatic islet. It was also shown in in vivo experiments that IL-1Ra can improve hyperglycemia, the function of β cells and the insulin resistance in GK rats. In addition, IL-1Ra can reduce the levels of the pancreatic islet-derived pro-inflammatory cytokines, such as, IL-1β, IL-6, TNFα, KC, MCP-1, and MIP-1α and infiltration of CD68(+), MHC II(+), and CD53(+) immune cells into the pancreatic islet. Expression of the cytokines in hepatic tissues is also reduced. Therefore, it was concluded that IL-1Ra could improve the function of β cells and may be used in treatment of type 2 diabetes.
Marc Y. Donath et al from the University of Zurich, Switzerland, conducted a double-blind clinical trial with anakinra, and it was discovered from the results that blockage of IL-1 can improve patient's hyperglycemia and functions of pancreatic islet β cells, and lower inflammatory markers in the blood. Furthermore, Marc Y. Donath et al also performed another double-blind clinical trail with an anti-IL-1 antibody XOMA 052 to evaluate its safety and pharmacokinetics. Patients in the trail showed excellent tolerance and no severe drug-related adverse reactions were reported.
In one study, 70 patients suffering from type 2 diabetes with A1C>7.5% and BMI>27 kg/m2 were randomly assigned to undergo treatment with anakinra or placebo for 13 weeks. Thirty-nine weeks after anakinra withdrawal, it had been shown that blockage of IL-1 with anakinra can lead to improvement of the proinsulin-to-insulin (PI/I) ratio and systemic inflammatory markers compared with values in placebo-treated patients, and the improvement can last 39 weeks after treatment withdrawal (Larsen et al, “Sustained Effects of Interleukin-1 Receptor Antagonist Treatment in Type 2 Diabetes”, Diabetes Care 2009, 32: 1663-1668).
Collectively, the inflammatory cytokines are one of important causes for onset of diabetes. In addition to the conventional treatments currently used, the anti-inflammatory treatment is likely to be a novel approach of diabetic treatment.
Since IL-1 in a trace amount can exert a full biological effect, the biological effect of IL-1 can be efficaciously suppressed when the concentration of IL-1ra is usually more than 100-folds higher than that of IL-1. During the course of treating rheumatoid arthritis, the dosage of anakinra is up to 100-150 mg/d, which imposes a very high requirement on the downstream processing and manufacturing in biopharmaceuticals and is a challenge to the biopharmaceutical corporations. In theory, IL-1Ra can act on IL-1 receptors at any sites in the body with no selectivity. And it is a question whether administration of a large dosage for a long time would lead to increased infection in the patients due to immunosuppression. In particular the patients with diabetes are susceptible to infection and uneasy to be cured. Frequent dosing adds the burdens on the body, mind and economy of patients. Furthermore, IL-1Ra has an in vivo half-time of only 4-6 hours, which curtails the efficacy and increases the dosage. Consequently, the trend of new drug development is to design a novel, targeted IL-1ra, improve the efficacy in diabetic treatment, reduce unnecessary immunosuppression, reduce the dosage, and extend the in vivo time of action.